# Circle Definition: Lesson for Kids

## Introducing the Circle

Do you remember the song 'If You're Happy and You Know It?' Start singing that song! Are you clapping, stomping and jumping? Now let's use the tune and change the words for 'The Circle Song:'

*A circle is a shape that is round.*

*A circle is a shape that is round.*

*A circle is a shape that is round,*

*And round and round.*

*A circle is a shape that is round.*

## What Is a Circle?

Now that you have circles on your mind, let's learn more about this interesting shape. A **circle** is a shape that is made up of a curved line. It's round, and all points on the curved line are an equal distance from the center point. This shape is two-dimensional, which means it's flat.

## Where Can You Find Circles?

Circles are very important parts of geometry, the study of points, lines and shapes; but they're important outside of geometry as well. In fact, you can find circles in everyday life--they're just about everywhere. Do you have a cup on your desk? The shape of the rim is probably a circle. Is there a round button on your shirt? That's probably a circle, too! And so is the letter 'o' you find in so many words.

You may have noticed that the circles listed are all man-made, but circles are also very common in nature. The rings around Saturn, the pupils of your eyes and the center of a flower are all circles that are made by Mother Nature.

One interesting thing about circles is that there are no **perfect circles**. A perfect circle is one where the curved line is exactly, *precisely* the same distance from the center point. Look at the button on your shirt. It may seem to be perfectly circular, but if you look very closely, you'll notice some small imperfections. The same goes for all other circles you encounter, even if you need to look under a microscope to notice those imperfections.

## Activity: Scavenger Hunt

As we talked about, circles can be found everywhere. There are probably countless circles waiting to be found all around your own home. Let's have a scavenger hunt to find some!

- Start outside. Try to find something shaped like a circle from just outside your door. It might be a ball laying in the yard or a tire on a car--from the sides, these look like circles.
- Now, look in your kitchen. There are many, many circles in the kitchen, like the rims of cups and bowls and the shape of plates. Some of your favorite cereals are circle-shaped, like Cheerios, and so are some crackers, pizzas and many fruits.
- Walk through the rest of your home and look for more circles. Door knobs and the clock on the wall are circles. See some change laying around? Quarters, dimes and pennies are circular. Keep looking and you might find much more.
- Lastly, look at your own body. Can you find any circles? Your eyes may be circles, as are the pupils on your eyes. The nostrils of your nose may even be circles.

## Lesson Summary

A **circle** is a two-dimensional shape that is made up of a curved line. It's round, and all points on the curved line are an equal distance from the center point. Circles can be found everywhere, but remember that **perfect circles** don't actually exist.

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## Kids Activity for Becoming Familiar with the Formal Definition of a Circle:

### Reminders and Facts:

- A circle is a round flat shape.
- The curved line that makes up a circle is called the edge of the circle.
- The center of a circle is the point that all of the points on the edge of the circle are the same distance from.

### Materials Needed:

- Masking tape
- A large open space of floor
- A measuring tape
- Pencil and paper

### Steps:

- Use the masking tape to create a circle on the floor.
- Have one student sit in the middle of the circle, and have the other students sit anywhere on the edge of the circle.
- Use the measuring tape to measure the distance from the student in the center to each student on the edge of the circle and have each student on the edge of the circle write down the distance on a piece of paper.
- Collect the pieces of paper and answer the activity questions.

### Activity Questions:

- What part of the circle does the student in the middle represent?
- What part of the circle are the students, other than the one in the middle, sitting on?
- What relationship do we find between the measurements that the students wrote down on each of their papers?

### Activity Answers:

- The student in the middle is at the center of the circle.
- The students other than the student in the middle are sitting on the edge of the circle.
- The measurements that the students took should all be very close to equal. This is because all of the points on the circle are the same distance from the center of the circle, and this demonstrates the definition of a circle as being a set of points that are all the same distance from a single point, which is the center of the circle.

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